This tutorial show you how to use the open source JUnit testing tool for Java to do Test-Driven Development (TDD). The promise of Test-Driven development is better software by thinking through how you want to test it, THEN writing code. At a high-level, you write enough of your class so that it runs. Then you think through how the class should work, and write test cases to test it. The test cases all fail because there’s no code. Finally, you write code until the test cases pass. And you’re done. So the testing of the software drives the entire process, which is why it’s called Test-Driven Development.